In 1938, when theKi-21heavy bomber began to enter service with theImperial Japanese Army, its capability attracted the attention of theImperial Japanese Airways. In consequence, a civil version was developed, and this, generally similar to the Ki-21-I and retaining its powerplant of two 708 kW (950 hp) Nakajima Ha-5 KAIradial engines, differed primarily by having the same wings transferred from a mid- to low-wing configuration and the incorporation of a newfuselage to provide accommodation for up to eleven passengers. This transport version appealed also to the navy, and, following the flight of aprototype in August 1940 and subsequent testing, the type was ordered into production for both civil and military use.[1]
This initial productionKi-57-I had the civil and military designations ofMC-20-I andArmy Type 100 Transport Model 1, respectively. A total of one-hundred production Ki-57-Is had been built by early 1942, and small numbers of them were transferred for use by the Japanese Navy in a transport role, then becoming redesignatedL4M1. After the last of the Ki-57s had been delivered, production was switched to an improvedKi-57-II, which introduced more powerful 805 kW (1,080 hp) Mitsubishi Ha-102 14-cylinder radial engines installed in redesignednacelles and, at the same time, incorporated a number of detail refinements and minor equipment changes. Civil and military designations of this version were theMC-20-II andArmy Type 100 Transport Model 2, respectively. Only 406 were built before production ended in January 1945. Both versions were covered by the Alliedreporting nameTopsy.[2]
Powered by two 708 kW (950 hp)Nakajima Ha-5 KAI radial engines and a redesigned fuselage to accommodate 11 passengers. About 100 aircraft of this type were built including the civil version.
Powered by two 805 kW (1,080 hp)Mitsubishi Ha-102 Zuisei 14-cylinder radial engines installed in redesigned nacelles. Minor equipment and detail refinements were also incorporated. 306 aircraft of this type were produced before the end of production in January 1945.
MC-20-II
Same as above but built for civil use with Imperial Japanese Airways (Dai Nippon Koku KK).
L4M1
A small number of Ki-57-Is were transferred for test by the Japanese Navy as transports and were redesignated L4M1.
On 20 December 1940, an Imperial Japanese Airways MC-20-I (J-BGON,Myuko) crashed into Tokyo Bay off Chiba during CAB's test flight, killing all 13 on board including 8 CAB inspectors.[citation needed]
On 21 June 1941, a Manchurian Air Transport MC-20 (M-604) crashed into theSea of Japan, killing all 18 on board.[citation needed]
Francillon, Ph.D., René J.The Mitsubishi Ki-21 (Aircraft in Profile number 172). Leatherhead, Surrey, UK: Profile Publications Ltd., 1967.
Francillon, René J. (1979).Japanese aircraft of the Pacific War. London: Putnam.ISBN0-370-30251-6.OCLC6124909. (new edition 1987 by Putnam Aeronautical Books,ISBN0-85177-801-1); 3rd edition 1987 by Putnam Aeronautical Books, 1987.ISBN0-85177-801-1).
1 X as second letter is for experimental aircraft or imported technology demonstrators not intended for service,2 Hyphenated trailing letter (-J, -K, -L, -N or -S) denotes design modified for secondary role,3 Possibly incorrect designation, but used in many sources
